Method of dezincing lead



Feb. 10, 1931. 0, BETTERTON 1,792,210

METHOD OF DEZINCING LEAD Original Filed May '7, 1926 awuemtoz 35 AL Gwen m5 2 metallurgical process. The lead Patented Feb. 10, 1931 UNITED" STATES PATENT OFFICE JESSE OATMAN BETTERTON, OF OMAHA, NEBRASKA, ASSIGNOR '10 AMERICAN SHELT- ING AND REEINING COMPANY, OF NEW YORK, N. Y., A CORPORATION OF NEW JERSEY .mn'rnon or DEZINCING LEAD- Originatapplication filed May 7, 1926, SerialNo. 107,325. Divided and this application filed November 1, 1926. Serial No. 145,402. r

This invention relates to a processfor refining metals, and more particularly, to a process for dezincing lead.

This is a division of the copending application of Jesse Oatman Betterton, Serial No. 107,325, filed May 7, 1926.

According to the invention, a metal having as an impurity metals electropositive to said metal,,is subjected in a novel manner to the action of a gaseous or other reagent, which,

unites with the more .electropositive metal to remove the same as a slag or dross.

- The process makes use of the fact that a reagent such as chlorine has a greater afiinity for certain metals, such as metallic zinc, than for other metals, such as metallic lead, when the metals are together in a molten state. For example, lead with zinc as an impurity therein may be the bullion resultin iullion may be that resulting from the Parkes process after the silver has been removed by the use of zinc. In lead resulting from the Parkes'process the amount of zinc remaining in the lead may be approximately 0.55 percent, or 11 pounds of zinc per ton of lead. In order to remove the zinc from the lead approximately 1.085 pounds of chlorine are required theoretically for every pound of zinc, and therefore for every 100 tons of lead-there would be required approximately 1,193 pounds of chlorine.

According to the invention, practically the entire percentage of zinc is removed by the use of little more than the theoretical amount of chlorine necessary to remove the zinc. This results in great economy of chlorine as well as great safety and comfort in refining, because of the fact that practically no unused chlorine escapes. The reaction of. the chlorine with the zinc produces considerable heat.

The zinc chloride formed by the reaction, and particularly the chlorine, are very corrosive at the temperature which is produced by the reaction, and are therefore very destructive to metal with which they come in contact. According to the invention, however, the process is so carried out that thechlorine and zinc chloride have no serious effect on the metal from any perature abovethe melting point of the lead and at a temperature which will cause the molten dross of zinc chloride to partially solidify on the surface of the bath, thereby forming a seal which tends to prevent the escape of chlorine in the form of volatile zinc chloride from the bath. The chlorine is supplied in amounts proportional to the'quantities of zinc or other impurities in the bath; and under proper conditions to prevent injury tothe walls of the reaction chamberor thepipes or the apparatus for maintaining circulation of the bath.

The reaction between the zinc in the lead bath and chlorine may simultaneous reactions:

Thus if any lead combines with the chloride to form lead chloride, the zinc will immediately combine with the lead chloride to be considered as. two

and

form zinc chloride and pure lead, provided suflicient zinc is still present in the bath.

The first skimmings of the kettle will be practically pure zinc chloride. skimmings, as the amount of zinc in the bath is decreased, however, may contain some lead chloride in addition to the zinc chloride.

The later This lead chloride may be skimmed off and I kept separate and may be used to treat subsequent charges of lead bullion containing zinc prior to treatment with chlorine gas.

The slag ma however, be removed in one skimming if esired' and the lead removed therefrom by passing the slag thru a quantity of molten zinc or molten lead containing an excess of zinc, Th reaction given in the third equation above will then take place producing commercially pure zinc chloride.

.Various other features of the invention will be obvious from the following particular description of the process and from the particular description of forms of apparatus for carrying out the process, or from an inspection of the accompanying drawings; and the invention also consists in certain new and novel steps of the process and new and novel features of the construction, and combinations of steps and of parts hereinafter' set forth and claimed.

The accompanying drawing illustrates a form of apparatus suitable for carrying out the process.

In the following description and in the claims arts. will be identified by specific names or convenience, but they are intended to be as generic in their application to similar parts as the art will permit.

Referring now to the drawing, the lead kettle 1 may be filled with molten lead con taining zinc to the height indicated by the line 14. Supported by the top rim of the kettle is a unit comprising a motor 2 and pump 3, the motor being supported by channel irons 4 extending across the kettle and resting upon the rim thereof. The pump is suspended from the motor and is located near the bottom of the kettle. The unit may be provided with a link 5 by means of which the unit may be carried about the plant, as from I this kettle to another kettle.

Supported also on the rim of the kettle 1 is a reaction cylinder 6 which may comprise a short length of pipe, the bottom of the cylinder being closed and having a discharge pipe 7 connected thereto which extends down beneath the surface of the bath a suitable distance. If desired this discharge pipe may not extend below the surface of the molten lead, but the discharge opening may be sealed tained in the bottom of the chamber to pre-' vent leakage of the gas. I may even submerge the entire reaction chamber beneath the surface of the molten lead. The reaction cylinder 6 may be supported by two I-beams 8 extending across the kettle, the I-beams having secured at their lower flanges transverse members 9 on which the reaction cylinder rests. The to of the reaction 0 linder may be provided with a flange 10 to which may be secured a cylinder head 11. A connecting pipe 15 may be connected from the discharge end of the pump 3 to the top of the head of the reaction cylinder, this pipe having a flanged union '16 for a purpose hereinafter described.

Located conveniently near the kettle may be the source of chlorine, which may be in the form of a chlorine tank 18 immersed in a vessel 19 filled with water and kept at an appropriate temperature. Suitable piping 20 mayconnect the chlorine tank with the reaction cylinder and a valve 21 may be provided for controlling the flow of the chlorine.

If desirable a ring of iron 12 may be provided to float on the surface of the bath to provide a restricted area in which the slag may be collected and removed.

In carrying out the improved process the motor and pump and also the reaction cylinder may be placed in the position shown after the kettle 1 has been filled to the level indicated, with molten lead. The parts of the connecting pipe 15 may be connected together by means of the flanged coupling 16, and the pump may be started and run for a few minutes to circulate the molten lead through the reaction cylinder to clean out any slag which may have adhered thereto from previous charges and also to warm up the cylinder. The pump is then stopped and the chlorine tank is connected to the reaction cylinder, and the chlorine turned on until it bubbles at the surface of the bath. The pump is then started and the chlorine valve .opened as far as possible without allowing the gas to escape at the surface of the lead.

Since the reaction of chlorine and zinc produces considerable heat, sufficient lead bullion must be kept circulating through the reaction cylinder .to prevent the temperature of the reaction cylinder from getting too high. This continuous circulation prevents corrosion of the reaction cylinder by the zinc chloride, and especially the chlorine, and washes the zinc chloride which is formed quickly through the discharge pipe and into the bath, where it floats to the surface in the form of a dross. In general, the cooling of the apparatus and the rate at which the heat is allowed to generate should be so arranged to give a temperature of about 670 degrees to 750 degrees F., at which temperature the improved process gives good results.

If the temperature is too high, the zinc chloride will volatilize quite ap reciably where'the lead bath is agitated or disturbed in any manner, as by the stream of lead discharged from the discharge pipe or by skimming off the zinc chloride; corrosion of the reaction cylinder by the chlorine and zinc .chloride is increased at a relatively high tem- Otherwise the process could be carried on at" i temperature near the melting point of the at w Preferablythe chlorine should bedelivered to the reaction cylinder under a slight pressure. For example, the chlorine tank was placed in water having a temperature of. to degrees F. This provided the proper conditions to cause the chlorine to be fed to the reaction cylinder at the desired rate of 200 to 250 pounds per hour, while the molten lead was circulated through the reaction chamber at the rate of 225 tons per hour. It will, of course, be appreciated that upon release of pressure the liberated gas will undergo a drop in temperatures The above figures are given by way of example only. Obviously the rate of circulation will depend upon the size of the apparatus used.

- When chlorine was fed at the above rate and the lead was umped through the reaction cylinder in tlie particular manner and with the particular apparatusnabove stated, thelevel of the lead in the reaction 0 linder was, for example, about 3ito 4 inches above the top of the discharge pipe. In general,

the rate of flow of the lead and the, other conditions should be arranged to allow a suf ficient space within the reaction cylinder to be filled with chlorine gas, through which the lead bullion may be pumped in a stream, to insure thorough mixing of the chlorine with the'impu're lead.

If chlorine is fed at, too great a rate to the reaction cylinder, it will be forced out the discharge pipe and may bubble through at the surface of the bath. On the other hand, if the chlorine is fed too slowly, the progress of dezincing is slowed down but no other detrimental effects result.

It will be evident from the foregoing that, in normal operation, for any given size of reaction cylinder and discharge pipe, the rate of passing the lead through the reaction cylinder may be varied over a definite range. The rate of feeding chlorine niay be varied both in relation to the speed of passing lead through the reaction cylinder and .the zinc contents of the lead at the particular time.

In order to maintain a maximum rate offeeding chlorine, advantage should be taken of increased speed .of pumping as the zinc. content decreases.

It has been found satisfactory to skim the dross or slag of zincchloridefrom the top of the bath in the kettle while running, since the top of the layer re-for'ms and freezes so rapidly that no appreciable loss of chlorine results. After practically all ofthe zinc is 130/removed from the bath, a white slag of lead chloride will appear. When this happens, the pump is stopped and when the chlorine bubbles through to the surface of the bath, the chlorine is shut off and the chlorine pipe disconnected. The pump is then started for a minute or so to insure that the reaction cylinder is thoroughly cleaned out. The kettle may be then skimmed clean. The chlorine pipe may be disconnected as above stated to prevent the chlorine piping 20 from filling with lead when the pump is started, and also to allow the escape of the chlorine from the reaction cylinder to the air when the pump is started, the chldrine in the cylinder being displaced by lead from the pump. Otherwise, if the chlorine pipe was not disconnected, the reaction cylinder would remain filled with chlorine and slag would be formed at the surface of the lead in the connecting pipe and discharge pipe. This would prevent starting later, and would subject the reaction cylinder to corrosion from chlorine and zinc chloride when the out of use.

Obviously if the cylinder is made sufliciently long the vacuum produced by the chlorine being absorbed by the lead will not cause the lead to rise to the'level of the chlorine pipe. In this case it will be unnecessary to disconnect the pipe although the chlorine should be shut off and removed from the cylinder by absorption or otherwise before allowing the apparatus to remain idle. in order to revent corrosion.

The final-slag on the surface of the bullion remains liquid much longer than previous slags, and as it does not freeze fast enough for skimming clean, and as it is too thin for ladling, considerable time may be lost in waiting for the slag to freeze if some remedy is not provided. In order to overcome this difiic'ulty, a button of pure cold lead may be placed in the kettle after the apparatus is removed to cool the lead bath sufiiciently for 0.003 percent zinc. There is practically no apparatus was loss of lead at the low temperatures at which the process is operated, since theselective act1on of the chlorine upon the zinc is more marked at low temperatures. The zinc ChlO-n,

ride is relatively pure and is in commercial form without subsequent refining or treatment. l

The material being treated is maintained in a relatively large pool in a receptacle having-a large radiating surface whereby a relatively low temperature can be maintained notwithstanding the heat of the re-action which occurs. Consequently, there is no excessive agitation of the bath in .the receptacle so that a layer of dross may readily form on topof the bath, which, in the case of zinc chloride, rapidl cools at atmospheric temperatures, there yforming a seal that preice ,method of practicing the invention, it is obvious that :the invention is not limited to this particular apparatus and method, but is broad enough to include any apparatus of any size and any method, so long as the broad teaching of the invention is followed. F urthermore, the invention is not limited to the purification of lead containing zinc by means of gaseous chlorine but is broad enough to include the 'purific tion of any material or metal by any kind of a gaseous or other reagent.

Having thus. described my invention, I claim: r

' 1, Method of refining a bath of molten lead containing zinc, which comprises confining precooled chlorine gas in a reaction tank, and continuously recirculating the metal ofthe bath through said chlorine while maintaining the-lower end of the tank sealed by the metal of the bath outside of said tank, to prevent escape of said chlorme.

2. Method of refining a molten metal, which comprises continuously feeding 'a gaseous reagent having the characteristics of chlorine to a reaction tank and continuously passing the molten metal through said reagent, the rate of passage being increased as the amount of impurities in the molten metal decreases. v

3. Method of refining a bath, of molten lead containing zinc, which comprises .feeddngchlorine gas to'a reaction tank, passing the metal of the bath through said chlorine,

the. rates of feeding said chlorine and passing said metal being regulatedto maintain the temperature between 670 and 750 de- 7 grees F.

4. The method of refining lead, which consists in forcingchlorine gas under slight pressure at a rate determined by the 1mpurities in the lead, and at a temperature below that'of the lead, into acyclic stream of molten lead and in a confined space separate from the bath of lead, returning said chlorine with the flowing metal, whereby the excess heat generated by the formation of the zinc chloride is removed fromthe cham continuous y recirculating the metal of the bath through said chlorine while maintain ing the lower end of the tank sealed by the metal'of the bath outside of said tank to vprevent escape of-said chlorine.

In testimony whereof I have hereunto set my hand.

JESSE oAi'rMAN BETTERTON.

stream into a bath of lead and collecting the chloride as a dross.

5. The method of continuously removing zinc from zinciferous lead, including heating a body of the lead to a temperature not exceeding the upper limit of the. range favoring the preferential formation of zinc chloride, c cling said lead through a closed reaction c amber in such quantities as to maintain the said chamber at substantially the same temperature as the body of circulating metal; admitting chlorine to the chamber under such conditions as to cool the reaction chamber, reacting the admitted 

